Applications of the Pt-190-Os-186 isotope system to geochemistry and cosmochemistry

New analytical techniques are utilized that permit the precise and accurate measurement of Pt-190-Os-186 isotope systematics. These techniques are applied to three different systems: sulfide ores associated with the 251.2 +/- 0.3 Ma Noril'sk, Siberia plume; the ca 4.55 Ga group IIAB iron meteorites, which are samples of an asteroidal core; and six enstatite chondrites. Isochrons are reported for the Noril'sk and IIAB systems. The results permit a precise determination of the decay constant of Pt-190. The Os-186 /Os-188 ratios for a variety of osmiridiums associated with ultramafic systems purportedly derived from the upper mantle, and the carbonaceous chondrite Allende was also determined. Both geochemical and cosmochemical applications of the system are discussed. (AIAA)